In recent years, in such fields as gene therapy and genetic screening, technologies of delivering small molecules such as nucleic acids to a cell are being actively developed. An example of the method of delivering nucleic acid to a cell is such that nucleic acid is encapsulated in a lipid membrane such as liposome, and delivering the nucleic acid to the cell by endocytosis or the like. As a liposome used to deliver nucleic acid into a cell, cationic liposome is studied and its application is progressing. Cationic liposome is a liposome comprising lipid having cationic properties and an auxiliary lipid which stabilizes the membrane, and is accumulated nonspecifically a cell membrane anionically charged. However, since nucleic acid is anionic and therefore sticks to a surface of a cationic liposome when encapsulating the nucleic acid in the liposome, it is difficult to encapsulate nucleic acid solely into a liposome. Here, in order to encapsulate nucleic acid into a liposome efficiently, a technique which binds nucleic acid with a peptide or the like and then encapsulated into a liposome is often used.
Under these circumstances, there is a demand of further development of the peptide which can encapsulate nucleic acid in a liposome more efficiently, and further development of the method delivering nucleic acid more efficiently to a cell.